The subject matter disclosed herein relates to valves and valve technology with particular discussion below that describes configurations of a valve assembly to provide automated and manual control of the position of a piston rod of a fluid-actuated device.
Many fluid systems incorporate a valve assembly to regulate fluid flow from a fluid supply to an actuator or like device. Systems with fluid-based actuators, e.g., hydraulic and pneumatic cylinders, may use the valve assembly to control the flow of working fluid to a cylinder. During operation, the working fluid flows into the cylinder to displace a piston rod to perform useful work, e.g., to move a load. In some applications, the actuator comprises a double-acting cylinder with two separate fluid inlets that are associated with a direction of travel of the piston rod.
Directional control valves are one type of valve assembly suitably configured to interface with the actuator to operate the cylinder. Valve assemblies of this type, also known as “spool valves,” have a housing with an inlet port that couples with a fluid supply and one or more outlet ports that couple with the fluid inlets on the cylinder. The spool valve can also have a moveable element (or “spool”) that translates to different positions in the housing. In some configurations, the spool valve is outfit with solenoids and/or a manual lever to move the spool. These devices can permit automatic operation and manual operation of the cylinder, as desired.
The position of the spool regulates the flow of the working fluid from the inlet port to the outlet ports to influence the direction of travel of the piston rod of the cylinder. The positions include open positions and closed positions. The open positions direct the working fluid from the spool valve to a first side of a piston coupled with the piston rod. In the open positions, the working fluid exhausts from a second side of the piston. The closed positions prevent flow and exhaust of working fluid to and from either side of the piston.
Conventional designs often utilize combinations of the open positions and the closed positions to obtain certain functionality for the spool valves. Two-position designs have two open positions for the spool. Movement of the spool between these open positions causes the piston rod to move between a maximum travel and a minimum travel. In three-position designs, the spool valve incorporates a closed position interposed between the two open positions. Locating the spool in this closed position can be used to control the travel of the piston rod, for example, to hold the piston rod at an intermediate travel between the minimum travel and the maximum travel.
Design specifications for a fluid system may mandate that the spool valve have different functionality for manual operation and automatic operation of the cylinder. For example, the specifications may call for a spool valve with functionality of the three-position design for manual operation and with functionality of the two-position design for automatic operation. Unfortunately, the two-position designs lacks the requisite closed position to allow the piston rod to be held at the intermediate travel. The three-position design, on the other hand, often includes a biasing element (e.g., a spring) that causes the spool to locate, or default, to the closed position from either of the open positions. This feature typically requires the solenoids to remain energized on the three-position design in order to maintain the spool in either of the open positions, which may not be desirable.
Due to the limitations of existing technology mentioned above, fluid systems need to combine multiple spool valves to achieve the dual-functions for manual operation and automatic operation. The resulting system would include, for example, one two-position spool valve for automated operation and one three-position spool valve for manual operation. This construction can add costs to incorporate the different-types of spool valves as well as complexity to the overall design of the system in the form of additional peripheral items (e.g., pipes, tubes, valves, etc.).